1. Technical Field
The present disclosure relates to a hearing aid, and more particularly, to a hearing aid attached to a mobile electronic device having improved use convenience, wherein elements forming the hearing aid are separated into a main hearing aid device and a sub-hearing aid device, the main hearing aid device is attached to the casing of a mobile electronic device and connected to the mobile electronic device through a wired cable for data transmission, and the sub-hearing aid device is placed in an ear of a user.
2. Related Art
Recently, as the average span of a man's life increases over 70 years or more, the demand for a hearing aid is gradually increased. The necessity for the hearing aid was recognized in the past, and the hearing aid was developed since the 1600s.
In the past, when a sound is not heard, a person can obtain an amplified sound of about 5 to 10 dB in an intermediate frequency or a high frequency by placing two hands in the auricles. In the 1600s, there was developed a hearing aid configured to have a wide sound collection unit, such as large Fallopian tubes, in order to collect sounds.
Thereafter, in the 1870s, a carbon hearing aid was developed based on the principle of a telephone. In the carbon hearing aid, if input voice pressure is changed over time, the density of carbon grains is changed and thus the resistance value of the carbon grains is changed. A change of the voice pressure over time is converted into a change in the waveform of the electrical signal of a voltage or current over time through a change in the resistance value of the carbon grains. The converted electrical signal is amplified, and the speaker of the hearing aid is driven by the amplified electrical signal. In this case, an acoustic gain of about 20 to 30 dB could be obtained.
In the 1920s, a hearing aid using a vacuum tube was developed. A change of voice pressure received through a microphone (i.e., a transmitter) having a coil connected to a magnet is converted into a change of an electrical signal through a movement of the coil of the microphone. The converted electrical signal is amplified through a vacuum tube amplifier, and the speaker of the hearing aid is driven by the amplified signal. In this case, an acoustic gain of about 70 dB could be obtained. However, the hearing aid using the vacuum tube is disadvantageous in that the size of a battery is large and heavy and difficult to use because it requires a high voltage of 100 V or more in order to drive the vacuum tube circuit.
In the 1950s, a hearing aid using a transistor was developed. A battery size is small because the transistor required a low operating voltage, and thus a circuit size is small. If such a transistor is used, a hearing aid having a small size may be fabricated. In particular, in the 1960s, an integrated circuit (IC) in which several transistors are embedded in a single chip was developed. Thereafter, hearing aids using the integrated circuits, such as a glasses type, a behind-the-ear (BTE) type, and an in-the-ear (ITE), were sequentially developed.
Thereafter, the size of the hearing aid was further reduced. In the 1980s, an external auditory meatus (in-the-canal (ITC)) type hearing aid that is fully put in an ear was developed. In the 1990s, an eardrum (completely-in-canal (CIC)) type hearing aid that is rarely noticed was developed.
The existing BTE type hearing aid is configured so that the entire hearing aid including a speaker is included in one earring module and an audio signal output by the speaker of the hearing aid is transferred to the eardrum of an ear through an air tube attached to the earring module. Thereafter, there was developed a receiver-in-canal (RIC) type hearing aid in which the speaker (i.e., a receiver) is separated from the hearing aid module of the earring type hearing aid, the speaker is placed close to the eardrum of the external auditory meatus within an ear, and the hearing aid module and the speaker are connected by two metal conducting wires.
Accordingly, the size of the hearing aid module can be increased compared to the ITE, ITC, or CIC type hearing aid by placing the hearing aid module behind an ear and placing the speaker (i.e., a receiver) within the ear. As a result, a control button for volume control and a battery having a relatively high capacity could be mounted on the hearing aid module, and the size of the hearing aid module was further reduced compared to the existing BTE type hearing aid. Accordingly, there are advantages in that a feeling of wearing is good and the hearing aid is rarely noticed by other people.
In recent years, with the significant development of the integrated circuit technology, a digital hearing aid in which all the circuits for a hearing aid function are basically implemented within one dedicated application specific integrated circuit (ASIC) chip is chiefly used. In the digital hearing aid, an electrical signal output by a microphone is made to pass through a pre-processing amplifier, a variable gain amplifier (VGA), and a low pass filter (LPF) and is converted into digital code through an analog-to-digital converter (ADC). Digital code suitable for the hearing characteristics of a person is output by applying various digital signal processing processes for the hearing aid function to the converted digital code. The output digital code is transferred to an ear of the person by driving the speaker through a digital-to-analog converter (DAC) or a class-D amplifier.
A signal processing algorithm used in such a digital hearing aid includes a directional microphone function for audio signals, a wide dynamic range compression (WDRC) function, an acoustic feedback cancellation function, a graphic frequency equalizer function, a noise reduction function, and a tinnitus (ringing) cancellation function.
From among the functions, the WDRC function refers to a function for separating a single microphone input signal into some frequency band signals, determining different threshold amplitude for each of the frequency band signals, amplifying the input signal with a linear-gain amplifier if input amplitude is smaller than the threshold amplitude and performing a log-linear compression if input amplitude is larger than the threshold amplitude at each of the frequency signal band, having different values of the linear-amplifier gain and the log-linear compression ratio for each of the frequency band signal, and adding the output signals of all the frequency band signals. Accordingly, the user of the hearing aid can well hear a signal of a wide amplitude range by greatly amplifying a signal having small amplitude and slightly amplifying a signal having great amplitude although a signal amplitude range in which the user may hear a signal when the user does not use the hearing aid is small. In the WDRC function, if threshold amplitude in all the frequency bands is set infinite and only an amplifier gain in each frequency band is different depending on the frequency band, the graphic frequency equalizer function can be performed.
The acoustic feedback is a phenomenon generated because both the microphone and the speaker are embedded in the hearing aid having a small size and thus the distance between the speaker and the microphone is close (usually within 2 cm). Thereafter, the audio signal output from the speaker is inputted to the microphone again, thereby being capable of generating a braying sound or echo, such as “whistling.” This is called the acoustic feedback. In particular, in order to prevent a phenomenon in which the user feels uncomfortable due to a difference between pressure in the external auditory meatus of the ear and atmospheric pressure transferred to the ear through the neck and nose if the hearing aid fully clogs the external auditory meatus, a ventilation hole that penetrates the hearing aid is always present in the hearing aid, such as the ITE, ITC, or CIC type. The acoustic feedback phenomenon is generated through the ventilation hole.
The hearing aid needs to be unnoticeable by other people because the user of the hearing aid does not want other people to know that the user uses the hearing aid. Accordingly, most of current hearing aid products are being developed in the form of the CIC type hearing aid that is greatly reduced in size and fully fit into an ear or the RIC type hearing aid in which the hearing aid and the speaker are separated and the hearing aid is rarely noticed due to a small size although the hearing aid is placed outside the ear
In general, the number of microphones mounted on one of the hearing aids is limited to 2 or 3 and the size of an embedded circuit and battery is also limited because the hearing aid is fully fit into the ear and the size of the hearing aid needs to be small enough so that other people rarely notices the hearing aid. It is advantageous that the number of chips forming a circuit for a hearing aid operation is a minimum because the circuit needs to be embedded in the hearing aid having a small size as described above. Accordingly, most of hearing aid manufacturers tend to implement all the circuits for the hearing aid within a single integrated circuit chip.
If surrounding noises are great, it is difficult for the user of the hearing aid to hear a required audio signal due to a masking phenomenon in cochleae. If a microphone array in which several microphones are regularly disposed in a one-dimensional or two-dimensional manner and a beamformer are used, surrounding noises can be removed with respect to at least a high frequency signal, and thus only an audio signal from a required direction can be heard. In an existing acoustic camera, a distribution of the intensities of audio signals can be displayed on a video signal relatively in detail using the microphone array and the beamformer. To this end, a microphone array including several tens of microphones is required. In existing hearing aids, the microphone array and the beamformer cannot be used because a maximum number of the microphones are commonly limited to 2 or 3 due to a limit to the size of the hearing aid.
Recently, as almost everyone carries at least one smart phone having a computer function added to a handheld phone, a technology in which the smart phone itself is used as a hearing aid was proposed KR Publication No 2014-0084744. That is, the hearing aid operation can be implemented by adding only application software without adding a separate hardware device to an existing smart phone in such a manner that a voice is obtained through the microphone of a smart phone, an application processor (AP) corresponding to the central processing unit (CPU) of the smart phone is used as a digital signal processor (DSP), and the voice output signal of the smart phone is transferred to an earphone through an earphone cable or Bluetooth wireless transmission.
However, a relatively long time is taken to drive application software for the hearing aid operation using only the AP of an existing smart phone because hearing aid signal processing-dedicated hardware is not embedded in the existing smart phone unlike in a hearing aid-dedicated DSP.
In general, it is known that a delay time taken for an audio signal to be delivered to an ear through a hearing aid device is less than 10 msec (0.01 second) in order for the audio signal to be not inconsonant to the ear. In this case, a single audio signal is separated into two audio signals of a sound component that is directly delivered to the ear without passing through the hearing aid device and a sound component that is delivered to the ear slightly late through the hearing aid device, and the separated audio signals are delivered to the ear. If a difference between the time taken for one of the two audio signals to be delivered to the ear and the time taken for the other of the two audio signals to be delivered to the ear is greater than 0.01 seconds, a corresponding person recognizes that the same audio signal is repeated twice because he or she recognizes the two audio signals as two different audio signals.
Furthermore, a person who has a severe hearing defect guesses what a counterpart says by seeing the counterpart's lip operations by his or her eyes. It is known that such a person feels very inconvenient if there is a great difference between the time taken for a sound to be guessed eye through lip operations and the time taken for a sound to be heard by the ear through the hearing aid. Accordingly, if a hearing aid is configured using only an existing smart phone without separate hardware, there is a disadvantage in that it is practically difficult to use the existing smart phone as the hearing aid because a delay time for signal processing is much greater than 0.01 seconds.
In order to solve such a problem, active research is being recently carried out in order to connect a smart phone and an existing hearing aid instead of using the smart phone itself as a hearing aid. Several companies have released hearing aids connected to Apple's iPhone in 2014.
FIG. 1 is a diagram illustrating a conventional hearing aid connected to a smart phone.
In FIG. 1, conventional hearing aids connected to a smart phone have been released under the name of “Made for iPhone Hearing Aids (MFi hearing aids).” In such hearing aids, a Bluetooth radio signal receiver has been added to existing hearing aids. In this case, an external audio signal can be received through the microphone of the existing hearing aid or a signal output by iPhone can be received through a Bluetooth receiver.
If a signal output by iPhone is received using the MFI hearing aid 120, a counterpart's voice can be heard more loudly and clearly by placing the iPhone 110 close to the counterpart, and a voice over the iPhone from the counterpart can also be heard more clearly because the voice is corrected according to the ear characteristics of a corresponding user through the existing hearing aid. Furthermore, there is an advantage in that several parameter values of the hearing aid that need to be controlled according to the ear characteristics of the user can be controlled relatively easily through an application (app) program executed in the iPhone.
However, it is necessary to satisfy a condition in which a delay time between the time taken for the iPhone to receive an audio signal through an iPhone microphone and the time taken for the audio signal to reach the ear of the user through the audio signal processing path of the iPhone and the signal processing path of the existing hearing aid must be smaller than 0.01 seconds. Furthermore, if a Bluetooth wireless device is used, there is a disadvantage in that the time taken to replace a battery is shorter in the MFI hearing aid than in an existing hearing aid because the consumption of the battery of the Bluetooth wireless device is twice or more than that of a near field magnetic induction (NFMI) wireless device.